5,918 research outputs found
Partonic Pole Matrix Elements for Fragmentation
A model-independent analysis of collinear three-parton correlation functions
for fragmentation is performed. By investigating their support properties it is
shown, in particular, that the so-called partonic pole matrix elements vanish.
This sheds new light on the understanding of transverse single spin asymmetries
in various hard semi-inclusive reactions. Moreover, it gives additional strong
evidence for the universality of transverse-momentum-dependent fragmentation
functions.Comment: 4 pages, 2 figures; minor changes, matches journal versio
Lorentz invariance relations and Wandzura-Wilczek approximation
A complete list of the so-called Lorentz invariance relations between parton
distribution functions is given and some of their consequences are discussed,
such as the Burkhardt-Cottingham sum rule. The violation of these relations is
considered in a model independent way. It is shown that several Lorentz
invariance relations are not violated in a generalized Wandzura-Wilczek
approximation, indicating that numerically their violation may be small.Comment: 10 pages; Proceedings of the workshop "Recent Advances in
Perturbative QCD and Hadronic Physics", July 20-24, 2009, at ECT*, Trento
(Italy), in honor of Anatoli V. Efremov on the occasion of his 75th birthday;
to appear in Mod. Phys. Lett.
Low-energy and low-momentum representation of the virtual Compton scattering amplitude
We perform an expansion of the virtual Compton scattering amplitude for low
energies and low momenta and show that this expansion covers the transition
from the regime to be investigated in the scheduled photon electroproduction
experiments to the real Compton scattering regime.
We discuss the relation of the generalized polarizabilities of virtual
Compton scattering to the polarizabilities of real Compton scattering.Comment: 13 pages, LaTeX2e/RevTeX, no figure
Structure analysis of the virtual Compton scattering amplitude at low energies
We analyze virtual Compton scattering off the nucleon at low energies in a
covariant, model-independent formalism.
We define a set of invariant functions which, once the irregular nucleon pole
terms have been subtracted in a gauge-invariant fashion, is free of poles and
kinematical zeros.
The covariant treatment naturally allows one to implement the constraints due
to Lorentz and gauge invariance, crossing symmetry, and the discrete
symmetries.
In particular, when applied to the reaction,
charge-conjugation symmetry in combination with nucleon crossing generates four
relations among the ten originally proposed generalized polarizabilities of the
nucleon.Comment: 19 pages, LaTeX2e/RevTeX, no figures, original sections IV.-VI.
removed, to be discussed in a separate publication, none of the conclusions
change
Relations between generalized and transverse momentum dependent parton distributions
Recent work suggests non-trivial relations between generalized parton
distributions on the one hand and (naive time-reversal odd) transverse momentum
dependent distributions on the other. Here we review the present knowledge on
such type of relations. Moreover, as far as spectator model calculations are
concerned, the existing results are considerably extended. While various
relations between the two types of parton distributions can be found in the
framework of spectator models, so far no non-trivial model-independent
relations have been established.Comment: 25 pages, 9 figures; Eq. (B17) and typos corrected, identical with
journal versio
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